This invention relates to Stirling cycle thermal devices and includes Stirling cycle heat engines and Stirling cycle heat pumps, and is particularly concerned with multi-cylinder Stirling cycle thermal devices.
In the Stirling cycle heat engine, on the application of heat energy to the hot chamber, a quantity of gas is cycled between intercommunicating hot and cold chambers by varying the chamber volumes. The resulting gas temperature changes cause a cyclic pressure variation which can be used to perform mechanical work if the total chamber volume is allowed to vary. The efficiency can be improved if the hot and cold chambers are interconnected through a regenerator which absorbs heat from the gas as it flows towards the cold chamber and replaces this heat when the gas returns.
Stirling cycle heat pumps on the other hand, although operating on the same principles as Stirling cycle heat engines, transfer heat energy from one chamber to the other when mechanical work is done on the gas. It should be noted that the direction of the transfer of heat from the heat intake end is the same whether the device is used as a heat engine or a heat pump. Thus the hot chamber of the heat engine and the cold chamber of the heat pump both absorb heat, heat being transferred in each case to the other chamber whose temperature is that at which the heat is rejected. In the interest of clarity, therefore, those chambers which absorb heat are hereinafter referred to as heat-absorbing chambers and those that reject heat are referred to as heat-rejecting chambers.
It is necessary when designing a Stirling cycle thermal device to achieve a cyclic volume variation in the heat-absorbing and heat-rejecting chambers, and to ensure that the correct phasing is maintained. The phase angle of the chamber which absorbs heat should lead that of the chamber which rejects heat by an angle which depends on the design of the device.
One known multi-cylinder variant of the Stirling cycle heat engine is the Rinia double-acting engine which uses connecting rods and rotating mechanical parts to derive mechanical power from the engine. The present invention seeks to provide a multi-cylinder Stirling cycle thermal device which possesses the thermal efficiency of the Stirling cycle without having the complication of mechanical systems hitherto used for utilising the mechanical power it develops.